Blender units vs metric
Inside Blender, 1 Blender Unit equals 1 meter, however, when importing, the software you are using could perceive arbitrary units as being equal to something other than 1 meter.

There are a couple of ways to solve this problem:

1. Change the Scene's scale factor

To do so, go to the Properties panel, then under the Scene tab, find the Units subsection and change the Scale field. 



When set to 1, 1BU = 1m, but if set to 10, 1BU = 10m; Pretty straight forward.

2. Change the exporter's scale factor

To do this, when exporting to .stl, before hitting Export, you can change the scale field, located on the bottom left corner.



3. Scale the object up in Blender

Hit S and the enter your scale factor/ratio, for instance 10, and the object will be 10 times bigger.

4. Scale the object up in the printing software

You figure that out.